1. Field of the Invention
The present invention relates to a developing roller to be used in an electrophotographic image-forming apparatus such as a copying machine and a laser printer, and an electrophotographic process cartridge and an electrophotographic image-forming apparatus which are provided with the developing roller.
2. Description of the Related Art
A contact developing method of making a developing roller carry a toner and abut on a photosensitive drum to develop an image is known as a developing method of visualizing an electrostatic latent image existing on the photosensitive drum with the use of the toner.
Many developing rollers provided with an elastic layer are proposed as a developing roller to be used for the contact developing method. This is because such a developing roller hardly damages a toner image formed on the surface of the photosensitive drum and can secure a predetermined quantity of nip width on an abutting portion against the photosensitive drum.
However, when such an elastic layer is a surface layer of the developing roller, the surface of the developing roller occasionally shows strong stickiness. When the surface of the developing roller shows strong stickiness (tackiness), a conveyed developer adheres to the surface of the developing roller, and becomes not easily detached. The developer remaining on the surface of the developing roller is repeatedly pressurized between the developing roller and the photosensitive drum, and is gradually deteriorated. As a result, the developer occasionally sticks to the surface of the developing roller. In order to inhibit the tackiness of the surface of the developing roller, Japanese Patent Application Laid-Open No. H09-62086 discloses an invention of depositing inorganic particles on the surface of the developing roller to enhance the release properties of a toner (developer). However, according to the investigation of the present inventors, these inorganic particles were easily detached from the surface of the developing roller, and it was difficult to maintain an effect of inhibiting the developer from sticking to the surface of the developing roller for a long period of time. In addition, the invention described in the above described Japanese Patent Application Laid-Open No. H09-62086 had difficulty in inhibiting a low-molecular-weight substance which was unavoidably contained in the elastic layer from bleeding to the surface of the developing roller.
Furthermore, the above described Japanese Patent Application Laid-Open No. H09-62086 discloses that a developing roller having a resin coating layer provided on the surface of the elastic layer was proposed as a conventional technique and that such a resin coating layer had insufficient flexibility and insufficient adhesiveness to the elastic layer, so that the resin coating layer might cause a crack or peeling due to change with time.